High severity · published Jul 14, 2026
CVE-2026-45304
Symfony: YAML Parser Exponential Memory Allocation via Recursive Collection-Alias Expansion ("Billion Laughs")
7.5
CVSS
0.7%
EPSS
No
On KEV
Description
Symfony is a PHP framework for web and console applications and a set of reusable PHP components. Prior to 5.4.52, 6.4.40, 7.4.12, and 8.0.12, Symfony\Component\Yaml\Parser resolved YAML collection aliases recursively, allowing a small untrusted YAML input to expand into a multi-gigabyte structure and exhaust memory. This issue is fixed in versions 5.4.52, 6.4.40, 7.4.12, and 8.0.12.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.7% · higher than 52% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
SY
symfony · symfony
< 5.4.52; >= 6.0.0-BETA1, < 6.4.40; >= 7.0.0-BETA1, < 7.4.12; >= 8.0.0-BETA1, < 8.0.12 · source: vendor, NVD
YA
yaml · symfony
< 5.4.52; >= 6.0.0-BETA1, < 6.4.40; >= 7.0.0-BETA1, < 7.4.12; >= 8.0.0-BETA1, < 8.0.12 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-45304
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-45304
Patch
https://github.com/symfony/symfony/commit/e77391b2e4f18821198f010d573674c8ed4a970a
Product
https://github.com/symfony/symfony/releases/tag/v5.4.52
Product
https://github.com/symfony/symfony/releases/tag/v6.4.40
Product
https://github.com/symfony/symfony/releases/tag/v7.4.12
Product
https://github.com/symfony/symfony/releases/tag/v8.0.12
Patch
https://github.com/symfony/symfony/security/advisories/GHSA-4qpc-3hr4-r2p4
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